1. Field of the Invention
Embodiments of the present general inventive concept relate to a sheet feeding device to provide optimum separating performance based on supplied sheets and an image forming apparatus including the same.
2. Description of the Related Art
An image forming apparatus forms an image on a sheet according to an input signal. The image forming apparatus includes a printer, copier, facsimile, and a multifunction device having functions of the printer, copier, and facsimile.
An electrophotographic image forming apparatus includes a photoconductor, an optical scanning device, and a developing device. The optical scanning device scans light to the photoconductor, which is charged with predetermined potential, to form an electrostatic latent image on the surface of the photoconductor. The developing device supplies a developing agent to the photoconductor, on which the electrostatic latent image is formed, to form a visible image. The visible image formed on the photoconductor is directly transferred to a sheet. Alternatively, the visible image is transferred to a sheet via an intermediate transfer device. The image transferred to the sheet is fixed to the sheet by fusing.
The image forming apparatus may include a sheet pickup device to pick up sheets loaded in a cassette or a tray one by one and a sheet supply device to feed picked-up sheets to a sheet feeding channel provided in the image forming apparatus. Two or more sheets may be picked up by the sheet pickup device and fed to the sheet feeding channel due to friction force of the sheets. Jam may occur in the image forming apparatus due to such multiple feeding of sheets.
In recent years, a retard type pickup structure has been developed. The retard type pickup structure includes a torque limiter and a retard roller connected to the torque limiter such that the retard roller is rotated forward or reversely according to the torque limiter to prevent multiple feeding of sheets. The torque limiter has a predetermined critical torque value. When sheet feeding friction force is greater than the critical torque value, the retard roller is rotated forward. When the sheet feeding friction force is less than the critical torque value, the retard roller is rotated reversely. The retard roller is disposed below the sheet feeding channel to prevent multiple feeding of sheets.
When no sheets are fed to the sheet feeding channel or only one sheet is fed to the sheet feeding channel, the sheet feeding friction force is greater than the critical torque value of the torque limiter. As a result, the torque limiter and the retard roller may be rotated in the sheet feeding direction to feed the sheet. When two or more sheets are fed to the sheet feeding channel, the sheet feeding friction force is less than the critical torque value of the torque limiter. As a result, the torque limiter and the retard roller are rotated in a direction opposite to the sheet feeding direction to prevent multiple feeding of sheets.
In a conventional structure, a reverse gear is provided to reversely rotate a retard roller or only the retard roller is provided without the reverse gear to achieve separation between sheets. However, the conventional structure may not provide a sheet separation area in which various kinds of sheets having different thicknesses, materials, and friction forces may are separated from each other.